This application claims priority under 35 USC xc2xa7119 to Japanese Patent Applications Nos. 2000-130049 and 2000-106146, filed on Apr. 28, and Apr. 7, both 2000, the entire contents of which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, a facsimile, etc., and in particular related to a charge member that contacts a surface of a photosensitive member and is capable of keeping high charge performance while preventing wear of a gap control mechanism disposed between the charge member and the photosensitive member.
2. Discussion of the Background
There is conventionally available a non-contact type charge unit based on a process of arranging the portion of the effective charge width of the charge member close to the surface of a photosensitive body serving as an image carrier and charging the surface of the photosensitive body by impressing a voltage between the charge member and the photosensitive body. This charge unit provides an advantage of being resistant to contamination because the effective charge width portion of the charge member does not come into contact with the surface of the photosensitive body. In a charge unit of this non-contact type, the portion of the charge roller other than the both ends is prevented from coming into contact with the surface of the photosensitive body serving as an image carrier by forming projections at both ends of the roller portion of the charge roller serving as a charge member through attachment of a tape member. An example of the charge roller is illustrated in FIG. 14. This charge roller 114 is formed by, for example, providing a conductive elastic portion 117 on the outer periphery of a core 116 made of stainless steel, and integrally fixing the same by winding resin tape members 118 and 118 in the circumferential direction on the both ends of the elastic portion 117.
The both ends of the core 116 are pressed with a prescribed pressing force against the photosensitive drum 105 via plain bearings 130 and 130 by means of pressing springs 119 and 119. In the charge roller 114, therefore, the tape members 118 and 118 come into contact with the surface of the photosensitive drum 105, and the effective charge width (Wac) of the elastic portion 117 prevented from being in contact with the surface of the photosensitive drum 105 (a gap G corresponding to the thickness of the tape member is formed).
However, the non-contact type charge unit, in which a prescribed gap is formed in the effective charge width between the charge roller thereof and the surface of the photosensitive drum by integrally fixing a tape member having a prescribed thickness at both ends of the charge roller, and bringing the tape member portion into contact with the photosensitive drum, has a problem of wear of the tape member.
More specifically, the gap G shown in FIG. 14 should have a size of, for example, about 100 xcexcm, or smaller than 100 xcexcm, since an excessively wide gap makes it impossible to obtain a prescribed charge performance. As a result, the tape member has a very small thickness of about 100 xcexcm. However, because the tape member continues rotating while the outer peripheral surface is in contact with the surface of the photosensitive drum, it is inevitable that the outer peripheral surface thereof is worn out with the lapse of time.
When the tape member prematurely is worn out, the charge roller comes into contact with the surface of the photosensitive drum at the portion of the effective charge width (a gap of null). In this state, residual toner on the photosensitive drum moves onto the portion of the effective charge width of the charge roller, and contamination thereof often results in defective charging.
On the other hand, even when the charge roller is prevented from coming into contact with the photosensitive body in the image forming area, the surfaces of the charge roller and the photosensitive body have fine concave and convex portions as represented by a straightness unavoidable in the axial direction in terms of processing accuracy (a value represented by the height from the bottom of a concave portion to the top of the convex portion; flatness when the object is flat). The charge roller and the photosensitive body may therefore be in contact with each other, depending upon the degree of straightness (or flatness).
Under these circumstances, even in a non-contact charge unit, when most part of the surface of the charge roller comes into contact with the surface of the image carrier, contamination adhering to the surface of the image carrier moves to the surface of the charge roller, thus deteriorating charge performance.
Accordingly, an object of the present invention is to address and resolve the above and other problems and provide a new image processing apparatus. The above and other objects are achieved according to the present invention by providing a novel image forming apparatus that may include a coated portion that forms a photosensitive layer, an image carrier that has a non-coated portions formed of a material harder than the coated portion on the both sides thereof, and a charge member that charges the coated portion of the image carrier. In addition, the charge member may be brought into contact with the surface of the image carrier via a gap control member in contact with a non-charged area of the coated portion of the image carrier to form a prescribed gap between a portion corresponding to an effective charge width of the charge member and the surface of the image carrier.
In another embodiment, a cleaning member may be provided to clean over a prescribed cleaning width by coming into sliding contact with the coated portion of the image carrier, and the gap control member may be positioned within the cleaning width of the cleaning member. The cleaning width may be outside or inside an outer end of the gap control member.
In yet another embodiment, a cleaning member oscillation mechanism may be provided to oscillate the cleaning member in a direction perpendicular to the sliding contact direction relative to the image carrier, and a cleaning oscillation area width of the cleaning member may be used as the cleaning width.
In yet another embodiment, the cleaning device may be provided to clean the coated portion by bringing a cleaning blade into sliding contact with the coated portion of the image carrier.
In yet another embodiment, a transfer member transferring a visible image formed on the surface of the image carrier may be provided, and an effective transfer width thereof may be narrower than the effective charge width of the charge member. In yet another embodiment, a development unit may be provided to develop a latent image on the image carrier with a developer into a visible image and the developing width is smaller than the effective charge width of the charge member.
In yet another embodiment, the development width may be smaller than the effective transfer width.
In yet another embodiment, the image forming apparatus may use a two-component developer using a toner and a carrier.
In yet another embodiment, the cleaning width may be wider than the effective charge width.
In yet another embodiment, a cleaning member oscillation mechanism may be provided to oscillate the cleaning member in a direction perpendicular to the sliding contact direction of the cleaning member relative to the image carrier, and displacement limits on the cleaning member may be located at positions outside the effective charge width, respectively.
In yet another embodiment, the charge member may include a charge roller having a metal shaft and an elastic portion on a portion other than both ends of its outer peripheral surface, and the gap control member may include a pair of tape members fixed to the both ends of the elastic portion, respectively. In addition, the width between insides of the pair of tape members may serve as the effective charge width. The tape member may be formed to have a thickness of up to 100 xcexcm.
In yet another embodiment, the pair of tape members may be wound and fixed to the both ends of the elastic portion in the circumferential direction, respectively in such a manner that there is no portion, in the roller axial direction, where the tape members are not present for all positions over the entire circumference without the both ends in the circumferential direction overlap.
In yet another embodiment, the inclination angle between the cut line of the both diagonally cut ends of the pair of tape members relative to the side edge of the tape members may substantially be 45xc2x0.
In yet another embodiment, the charge roller may have the both ends of the metal shaft spaced apart from the non-coated portion at positions where no leakage is caused from the both ends of the metal shaft to the non-coated portion of the image carrier when voltage is impressed between the metal shaft and the image carrier.
In yet another embodiment, the charge member may include a charge roller having of the metal shaft and an elastic portion at a portion other than the both ends of its outer periphery, and the gap control member may include a pair of rollers attached to the both ends of the metal shaft.
In yet another embodiment, an image carrier unit may provided to integrally mount the image carrier and the charge member.